Packages and Package Diagrams

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Packages and Package Diagrams

• Keng Siau
• University of Nebraska-Lincoln

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Packages

• A package is a general-purpose mechanism for
  organizing modeling elements into groups
• It has no meaning to the execution
• Well-designed packages group elements that are
  semantically close and that tend to change
  together
• Loosely coupled and very cohesive
• Graphically, a package is rendered as a tabbed
  folder

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Packages
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Names

• Each package must have a name that distinguishes
  it from other packages
• A name is a textual string
• Two types of names
• Simple names e.g., Business rules, Client
• Qualified names SensorsVision
• Package name prefixed by the name of the package
  in which that package lives

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Simple and Qualified Names
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Owned Elements

• A package may own other elements
• Classes, interfaces, components, nodes,
  collaborations, use cases, diagrams, and other
  packages
• Ownership is a composite relationship
• If the package is destroyed, the element is
  destroyed
• Every element is uniquely owned by exactly one
  package

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Owned Elements and Visibility

• Visibility
• Public element is visible to the contents of any
  package that imports the elements enclosing
  package
• Prefixed the name with a symbol
• Protected element can only be seen by children of
  that package
• Prefixed the name with a symbol
• Private element is not visible outside the
  package at all
• Prefixed the name with a - symbol

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Importing and Exporting

• Two stereotypes
• Import adds the contents of the target to the
  sources public namespace
• Access adds the contents of the target package to
  the sources private namespace
• The public parts of a package are called its
  exports

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Importing and Exporting
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Packages versus Classes

• Classes are abstraction of things found in the
  problem or solution
• Packages are mechanisms to organize things in the
  model
• Packages do not appear in a running system
• Strictly mechanisms to organize the design
• If one is developing a trivial application, there
  is no need for packages

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Modeling Groups of Elements
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Example of a Package Diagram